In document copiers a duplexing operation refers to the provision of copies which carry document images on both sides of the copy sheet and collating refers to automatically organizing multiple sets of multi-page document copies in correct order. Several patents have issued which relate to apparatus for automatically performing the duplexing function, for example, U.S. Pat. Nos. 3,645,615; 3,851,872; 3,856,295; 3,615,129; and 3,917,256. All of these patents relate to an automatic duplexing operation, perhaps in conjunction with collating as well, when processing paper in the wide direction, e.g., the 11-inch direction for 81/2 .times. 11-inch paper. These patents relate to the electrophotographic copier machine of the transfer type in which an image is typically produced on a rotating drum, the image is developed, the developed image is transferred to a sheet of copy paper and finally the image is fused to the copy paper. It is evident in this process that the leading edge of the copy paper must be mated to the leading edge of the image in order that the image may be transferred to the copy paper. Since all of the above-referenced prior art utilizes the wide side of the copy paper as the leading edge, if one wishes to copy on the reverse side of the copy paper, all of this prior art shows mechanisms to turn the paper over and utilize the opposite wide edge (e.g., 11-inch edge) as the leading edge on the second pass. In that manner, the top of a copy sheet containing printed word line matter is maintained on both sides of the copy sheet, assuming that the printed word lines read downwardly with the narrow dimension of the paper at the top.
Perhaps the major reason for the adoption of the wide side of the copy paper as the leading edge in automatic duplexing operations is that it is relatively simple to perform the necessary paper orientation in that system to maintain the top on both sides. Where the wide edge leads, as the copy paper leaves the fuser it is simply turned under (or over) the fuser, which turns the paper over and sends it back toward the drum; typically, the paper continues to move past the drum (under or over the drum), whereupon the paper is simply stopped and reversed toward the drum for copying on the second side. This paper reversal obviously causes the opposite edge to lead through the transfer station and therefore a correct duplexing operation is accomplished. However, when processing paper with the narrow edge leading, for example, the 81/2-inch edge of an 81/2 .times. 11-inch paper, the above duplexing scheme will not work since it results in the print on one side of the paper reading upside down to the print on the second side. For example, if the narrow leading edge is turned under the fuser, according to the above scheme, and returned past the drum, and if the top of the copied image is near the leading edge, and if now the opposite edge is made to lead into the drum, the top of the second side is printed oppositely to the bottom of the first side. It is, therefore, the primary object of this invention to provide a method and apparatus through which automatic duplexing may be accomplished together with a collating function for both simplexed and duplexed copies, where the leading edge of the copy paper is maintained during both passes through the copier. It is a further object of the invention to provide as simple a paper handling procedure and apparatus as possible.